A car navigation apparatus holds map data including road data, facility data, and so on, and uses these map data to realize functions such as calculating and displaying a vehicle position, searching for a route to a destination, and providing guidance along the route. However, road data relating to an existing road may not be included in the map data, and in this case, the above functions cannot be realized.
In response to this problem, methods of adding road data relating to a road that is not included in the map data to the map data have been proposed. For example, Patent Document 1 discloses a vehicle navigation apparatus which makes route searches, route guidance, and so on that are useful to a user possible by updating map data without increasing a load on the user. In this navigation apparatus, map data stored on a CD-ROM, a DVD-ROM, or the like are updated by generating and storing new road information based on data relating to a traveling locus of the vehicle throughout the duration of a condition in which the vehicle is determined to be traveling on a road that does not exist in the map data, whereupon the updated map data are used for map display, route searches and route guidance.
Further, errors in the traveling locus may lead to cases in which incorrect roads are added to a map, and as a technique for preventing this problem, Patent Document 2 discloses a vehicle display apparatus which, when the vehicle travels on a new road not included in an existing map database, updates road data even if the vehicle only travels on the road once, rather than repeatedly, provided that position information is reliable. This vehicle display apparatus has a navigation function, and when the vehicle travels on a new road not included in the map database for the first time, the apparatus determines the reliability of vehicle position information from a number of receivable satellites and so on. When the positional accuracy is reliable, the road is recognized and registered in the form of road data. Thereafter, the new road serves as a display and route search subject.
Further, Patent Document 3 discloses a vehicle navigation apparatus which, when map data relating to the temporary road are generated, allows a user to use the temporary road flexibly in certain cases after the user has acknowledged that a problem exists in the reliability of the map data. In this vehicle navigation apparatus, a temporary road map data generation unit generates temporary road map data on the basis of processing results from a locator unit, a map matching unit, and a road deviation determination unit. The generated temporary road map data are registered in a map database by a temporary road map data registration unit. At the time of registration, a temporary road flag is attached to the temporary road map data, and a link of an official road to which the temporary road is connected is divided into a plurality of links. Divided link data are then registered in the map database with a post-division flag attached, while undivided link data are left in the map database with a pre-division flag attached.    Patent Document 1: Japanese Unexamined Patent Application No. 2004-251790    Patent Document 2: Japanese Unexamined Patent Application No. 2003-130656    Patent Document 3: Japanese Unexamined Patent Application No. 2006-242754
The conventional techniques described above have the following problems. In the technique disclosed in Patent Document 1, road data relating to a new road are generated on the basis of vehicle traveling locus data throughout the duration of a condition in which the vehicle is determined to be traveling on a road that does not exist in the map data, and the map data are updated by adding the generated road data thereto. Hence, an incorrect road may be added to the map due to errors in the traveling locus or the like.
Further, in the technique disclosed in Patent Document 2, the reliability of the vehicle position may not always be determined correctly, and in locations where the number of receivable satellites is limited due to the effects of peripheral buildings, roads, and so on, road data cannot be added. Furthermore, in the technique disclosed in Patent Document 3, the user chooses whether or not to use an added road, and it is therefore impossible to use only correct roads.